Method for applying covering material to an elongate substrate

ABSTRACT

Wrapped covering material, e.g. tape is applied around an elongate substrate, such as a pipe, using an apparatus comprising a hollow frame mounted on rollers that is rotatable about the substrate, a delivery device for holding the covering material, mounted on the frame, and pressure rollers designed to press down on the covering material.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an apparatus and method for applying a wrappedcovering material around an elongate substrate or around a joint betweensuch substrates, and in particular to an apparatus and method forapplying tape or a wraparound sleeve around pipes or cables (or jointsbetween pipes or between cables) in a void-free manner.

2. Introduction to the Invention

It is well known to wrap covering material around elongate substratessuch as pipes or cables or joints therebetween in order to provide aprotective coating, for example against corrosion or mechanical abuse orother environmental factors. One common example where a protectivecoating is required is where metal pipelines, factory coated with a thinpolymeric outer layer (known as a mill coating), are joined by weldingin the field. The mill coating is traditionally a sintered or extrudedpolyethylene layer. More recently multi-layer coatings comprisingsequentially a fusion bonded epoxy layer, a hot melt adhesive layer andan outer polyethylene layer have become popular. Typical mill coatingsare 1.5 to 9 mm thick. In order to form the weld, the mill coating,whatever its nature, must first be removed. This means that after thewelding there is a bare pipe portion around the weld that needs to beprotected. Solutions to this involve wrapping tape, e.g. polymeric tape,or a wraparound polymeric sleeve around the bare portion. Where awraparound sleeve is used this may be heat recoverable (preferably heatshrinkable), and may be closed around the pipeline by an adhesive coatedpatch closure as described for example in U.S. Pat. No. 4,359,502,European Patent Publication No. 23,788, and European Patent PublicationNo. 163,508, and as also described, for example, in Raychem's WPC(Wraparound Pipe Sleeve) installation instructions. By a heatrecoverable article is meant one whose dimensional configuration may bemade to change when subjected to an appropriate treatment. Usually thesearticles recover, on heating, towards an original shape from which theyhave previously been deformed, but the term "heat recoverable" alsoincludes an article which, on heating, adopts a new configuration, evenif it has not been previously deformed. Typically heat-recoverablearticles comprise a radially heat-shrinkable sleeve exhibiting theproperty of elastic or plastic memory, as described, for example, inU.S. Pat. No. 2,027,962, U.S. Pat. No. 3,086,242, and U.S. Pat. No.3,597,372.

In order to achieve good bonding of the tape or sleeve to the pipelineit is known to preheat the substrate (in the case of an applied heatrecoverable tape or sleeve) or to use epoxy primers applied to thepipeline before application of the sleeve or tape as described forexample in European Patent Publication No. 181,233, the entiredisclosure of which is incorporated herein by reference. Even with theseadditional precautions it is sometimes possible for air voids to betrapped between the covering sheet or tape and the underlying substrate,which may be undesirable in some circumstances. To remove or at least tominimize these voids it is known to use a hand-roller to roll out thevoids in the heat-installed heat shrinkable sleeve or tape or in thecold-installed wrapped tape. Preheating of a substrate prior toinstallation of a heat-shrinkable sleeve, and hand-rolling of the shrunksleeve, are both described, for example, in the above mentioned RaychemWPC installation instructions. While hand-rolling can be effective it istime consuming and, of course, installer sensitive.

SUMMARY OF THE INVENTION

We have made, accordingly to the present invention, an apparatus whichcan be used both to deliver a covering material such as tape or a sleeveto an elongate substrate, and also to apply a radially inward pressureon the delivered covering material, so that a void free installation canbe automatically achieved without depending on an installer hand-rollingto eliminate voids.

Thus a first aspect of the invention provides an apparatus for applyinga wrapped covering material to cover an elongate substrate or a jointbetween such substrates, comprising:

(a) a hollow frame which can be positioned around the elongatesubstrates(s), and which is mounted on two or more wheels or rollersthat, in use, can be rolled around the substrate(s) causing the frame torotate relative to the substrate(s);

(b) a covering material delivery device mounted on the frame, forreceiving the covering material and for delivering it onto the surfaceof the substrate(s) as the frame is rotated; and

(c) one or more pressure rollers that may be the same as, or additionalto, the rollers defined in (a), the rollers being arranged to pressradially inward onto the delivered covering material as the frame isrotated.

A second aspect of the invention provides a method of applying a wrappedcovering material around an elongate substrate or a joint between suchsubstrates comprising:

(a) positioning the apparatus according to the first aspect of theinvention around the substrate(s) so that the frame surrounds thesubstrate(s) and the wheels and/or rollers rest on the substrate;

(b) mounting the covering material in the delivering device; and

(c) rotating the frame relative to the substrate thereby delivering thecovering material and causing the pressure roller(s) to press radiallydownward on the covering material.

DETAILED DESCRIPTION OF THE INVENTION

According to the invention the frame surrounds the substrate. By this ismeant that the frame may surround the entire periphery of the substrate(i.e. around 360°), or may surround only part of the periphery of thesubstrate.

The frame may be rotated relative to the substrate by rotating theframe, rotating the substrate, or both.

The present invention advantageously achieves an installation that canbe fully automatic, can provide an essentially void free installationand can also be significantly faster than the prior art hand-rollingtechnique. Another advantage of the automatic nature of the delivery andpressure applied is that uniform application of pressure can be providedover the whole surface of the elongate substrate. This is in contrast tohand-rolling, where the installer does not always have equal access toall sides of the substrate, and also tends to concentrate on "problemareas", especially where the elongate substrate to be covered is large,resulting in non-uniform pressure application.

The covering material is preferably a tape or a wraparound sleeve. Itmay be wrapped circumferentially around the substrate(s), or helically.In order to wrap the covering material circumferentially, the apparatusis arranged, similarly, to move circumferentially around the substrate.If the covering material is to be wrapped helically the apparatus isarranged to move longitudinally as well as circumferentially around thesubstrate(s) in order to achieve this.

The delivery device for the covering material may be any suitableconfiguration. It may for example comprise a spool or the like on whichthe covering material is rolled. The material is then simply unrolledfor delivery.

The roller(s) preferably comprise a resilient material such as siliconerubber or the like. The resilience enables the roller to conform to anybumps on the substrate(s). Preferably a layer (preferably the outerlayer) of resilient material is provided on the roller. This preferablyhas a hardness in the range of shore A 30-60, and a thickness in therange of 15 to 50 mm. This resilience and thickness enable the roller toaccommodate and conform to small irregularities in the surface of thesubstrate as it presses the covering material against the substrate.

Preferably the frame and roller(s) are so arranged that the roller(s)press the covering material firmly against the underlying substrate.Preferably the roller(s) extend generally parallel to the axis of thesubstrate, and roll around the circumference of the substrate. In onepreferred embodiment, one (or more) rollers can be moved from a firststop position to a second stop position relative to the frame, whereinwhen the roller is in the first position it is further from thesubstrate than in the second position. Preferably the arrangement issuch that in the first position the roller does not press on thesubstrate, but in the second position it does. Thus, for example, theroller may extend, generally parallel to the axis of the substrate,between bars that are pivotally fixed to the frame, whereby the bars canpivot in a plane substantially perpendicular to the axis of thesubstrate to move the roller(s) between the said first and secondpositions. In addition, or instead, the roller(s) may be resilientlybiased against the covering material and underlying elongate substrate.Other equivalent biasing means could also be used as would be evident tothe man skilled in the art.

Preferably the frame and rollers are arranged such that the roller(s),or at least one of the rollers, exert a radial pressure of about 20Kg/cm² on the underlying covering material and elongate substrate(s).

One application where it is particularly preferred for more than oneroller to be used is where a wraparound sleeve is to be wrapped around awelded joint between two coated metal pipes which have been bared ofcoating in the weld region, e.g. a welded joint between two mill coatedsteel pipes. In this case a ridge is produced around the weld, theso-called "weld bead", and two further size transitions exist on eitherside of the weld bead at each bared edge of the (mill) coating. Where asleeve is wrapped around such a welded joint the weld bead and (mill)coating transitions are common areas where voids may form. According toa preferred embodiment of the present invention the apparatus and methodmay be arranged so that one roller acts on the weld bead region, andanother roller (or two other rollers) acts on the transitions betweenthe pipe coating and the bare pipes. The use of separate rollers meansthat the appropriate pressure can be applied in each position toeliminate voids. The appropriate pressure to be applied is differentover the weld bead and over the coating/bare metal transitions becausethe size and shape of each is different.

Where two or more rollers are used, their swept areas, (i.e. the areasthat they roll over when the frame is rotated) are preferably arrangedto overlap, or at least to meet. This ensures that there is no area ofunrolled delivered covering material.

The frame of the invention is positioned around the elongate substrate.It may be slid over one end of the substrate. In general, however, afree end of substrate is not available. In these cases, therefore, theframe can preferably be positioned around the elongate object(s) fromone side. As one example, the frame may be arranged to be a wraparoundconfiguration, for example hinged, with some sort of holding mechanismto hold the frame closed. As another example, where two or more rollersact both as the frame's wheels and as the pressure rollers, and one ormore of the rollers can be moved from a first stop position where itdoes not press against the substrate to a second stop position where itdoes press against the substrate, then the arrangement is preferablysuch that with the roller in the first stop position the frame can bebrought into position from one side of the substrate, and with theroller in the second stop position the frame is held against thesubstrate (so it does not fall off when rotated around the substrate).

The apparatus and method according to the invention can be used to applytape or sleeves that are non-heat-recoverable, slightly heat recoverable(e.g. less than 5% recovery) or heat recoverable of say 10-70%especially 15-50%. Where a recovery ratio is defined in terms of apercentage, the ratio represents the change in a dimension as apercentage of the same dimension before recovery.

The apparatus and method can be used where preheating of the substrateis required or where no preheating is required. Preheating may typicallybe required, for example, to apply a sleeve or tape (which may or maynot be heat recoverable) that is coated with a heat-activatable adhesivesuch as a hot melt adhesive. Especially suitable hot-melt adhesivesinclude, for example, polyamides, ethylene vinylacetate copolymers andterpolymers (with or without incorporated waxes) and polyesters. Nopreheating may be needed to apply tapes or sleeves coated with asealant, such as a mastic.

Where preheating is used, the pipeline typically needs to be preheatedto above 100° C., sometimes 150° C., 200° C. or even 220° C. In oneembodiment according to the invention, preheating is used in combinationwith slightly heat-recoverable covering materials (i.e. less than 5%recovery). In this case the recovery temperature of the coveringmaterial may be arranged to be lower than the preheating temperature, sothat the heat applied to preheat the elongate substrate can also effectrecovery of the covering material. A small amount of recovery may bedesirable in the covering material to compensate for any thermalexpansion of the sleeve during installation.

The apparatus and method according to the invention can also be used inapplications where there is no heat applied, either preheat or heat toshrink a sleeve. As an example, it can be used to apply helicallywrapped overlapping tape and to apply pressure to the overlap region ofthe tape, or to cold-applied sleeves. Indeed we have found that usingour invention a good bond can be achieved between some mastic coatedsleeves and a pipeline without preheating of the pipeline, even thoughwith prior art techniques (e.g. hand-rolling) preheating was required toachieve the same bond.

Where preheating is carried out, this may advantageously be done by useof an induction heater positioned around the substrate before the frameis put into position. Alternatively the heater may be positioned on theframe.

The apparatus and method can also be used to deliver covering materialhaving a recovery ratio greater than 5%, e.g. 15-70%. In this case it ispreferably delivered by the apparatus according to the invention andthen heated to effect recovery. In this case if preheating is alsocarried out, the preheating is preferably to a temperature lower thanthe recovery temperature of the covering material, so that full recoveryof the covering material does not take place at the preheating stage.

In certain applications of the invention, it is desirable to combine apreheating of the pipe with preheating also of the adhesive coatedcovering material, before it contacts the pipeline. As an example thepipe may be preheated to the temperatures indicated earlier, e.g. to atemperature in the range 140° to 160° C., and the coated coveringmaterial heated to about the tack temperature of the adhesive coating onthe covering material. This tack temperature will depend on the materialof the adhesive. It may be in the range 140° to 180° C., e.g. 150° to170° C. A suitable arrangement for heating the covering material (e.g.tape) before it contacts the pipeline is to position an infrared heaterbetween the delivery device for the covering material and the pressurerollers. This infrared heater may be supported on the frame.

Where preheating of the adhesive-coated covering material is carriedout, the speed of the pay-off of the covering material from the deliverydevice is preferably substantially matched to the speed of the relativerotation between the frame and the pipeline, so that the coveringmaterial (which may soften at the elevated preheat temperatures) is notstretched or allowed to shrink before it contacts the pipeline.

One advantage of the preheating of the coated covering material is thatwhen the heated adesive contacts the pipeline it will adhere better tothe pipeline than if it had not been preheated. Similarly where thecovering material is helically applied with overlapping edges, e.g.helically wrapped overlapped tape, the adhesive adheres better in theoverlap region than if it had not been preheated. Another advantage isthat the preheated covering material is softer than a non-preheatedcovering material. Therefore it can conform more easily toirregularities in the pipe surface. These advantages are particularlyuseful where the covering material is applied over a joined pipelinewith a protruding weld bead. Usually weld beads project radiallyoutwards as an annular flange (e.g. about 4 mm), and it is common tosmooth the transition at such weld beads by using a weld bead filler,e.g. a mastic, positioned around the bead. Such a filler avoids theproblem of a tent-shaped void appearing beneath a covering material overthe weld bead. However, we have found that by using a preheated coveringmaterial in the way described it is possible to avoid the need for aweld bead filler.

Where covering over weld beads is concerned, and in other applications,it may be useful to include a "following" roller which acts on the sameregion of covering material as the first "leading" roller, or on asmaller or on a larger region. Where a roller is used over a non-uniformsurface, e.g. a tape overlap region or a weld bead, it may have abevelled lower surface.

Where temperatures of about 130° to 170° C., e.g. 140° to 160° C., areused to preheat the pipe and the covering material and to form theinitial bond between the pipe and covering, it may also be desirable touse an induction heater to heat the surface of the pipe to a highertemperature of say 200° C. or 240° C. for a few seconds to ensure a goodbond to the pipe. This method ensures that only the bonding surface isheated to 200° C. or more, and this heat is rapidly distributed throughthe heat sink of the pipe. Therefore the overall temperature of the pipeadvantageously does not need to be heated to such high temperatures.

The combined preheating of substrate and the adhesive-coated coveringmaterial provide another aspect of the invention.

Thus a futher aspect of the invention provides a method of applying awrapped covering material around an elongate substrate or a jointbetween such substrates comprising:

(a) positioning an apparatus comprising

i) a hollow frame which can be positioned around the elongatesubstrates(s), and which is mounted on two or more wheels or rollersthat, in use, can be rolled around the substrate(s) causing the frame torotate around the substrate(s);

ii) a covering material delivery device mounted on the frame, forreceiving adhesive-coated covering material and for delivering it ontothe surface of the substrate(s) as the frame is rotated;

iii) one or more pressure rollers that may be the same as, or additionalto the rollers defined in (i), the rollers being arranged to pressradially inward onto the delivered covering material as the frame isrotated; and

iv) a heater, preferably an induction heater, for heating theadhesive-coated covering material before it contacts the pressurerollers

so that the frame surrounds the substrate(s) and the wheels and/orrollers rest on the substrate;

(b) mounting the adhesive-coated covering material in the deliverydevice;

(c) preheating the substrate to 130° to 170° C.;

(d) preheating the adhesive-coated covering material to about the tacktemperature of the adhesive with the said heater; and

(e) rotating the frame relative to the substrate thereby delivering thecovering material and causing the pressure roller(s) to press radiallydownward on the covering material.

While the apparatus and method can be used with heat recoverablecovering materials an advantage of the invention is that a fight fit ofcovering material about an elongate substrate can be achieved withoutthe need to use heat recoverable coverings, or at least to use onlythose with recovery less than 5% ( to compensate for thermal expansion).This is cost and time effective since it eliminates the expansion steptypically required to render a heat-recoverable covering materialrecoverable.

Another advantage of the tight wrap achieved by the present invention isthat material usage is minimized, which is cost-effective.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example,with reference to the accompanying drawings; wherein

FIG. 1 is a cross sectional view through a welded joint between twopipes which is to be covered using an apparatus and method according tothe invention;

FIGS. 2 and 3 are a side elevation and a plan view respectively of afirst apparatus according to the invention suitable for covering thejoint of FIG. 1;

FIGS. 4 and 5 are plan and side views of the rollers of the apparatus ofFIG. 2 applied to the welded joint of FIG. 1;

FIG. 6a is an enlarged side view of the application of the rollers ofFIGS. 2 to 5 to apply the covering material to the welded joint of FIG.1;

FIG. 6b is a side view of the covering material;

FIG. 7 is a perspective view of a second apparatus that can be used tocover the joint of FIG. 1;

FIG. 8 is an end view of the apparatus of FIG. 7 positioned around thejoint of FIG. 1; and

FIGS. 9 and 10 are side views of the apparatus of FIG. 7, at differentpositions of its rotation around the substrate of FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring now to the drawings, FIG. 1 shows two steel pipes 2 weldedtogether. The weld bead 4 projects in a ridge above the surface of pipes2, typically by a height of 4 to 5 mm. Typically the weld bead 4 isabout 18 mm in width. In order to form the weld the mill coating 6 oneach pipe 2 has been bared at the weld region. Typically each millcoating is about 6 mm thick, and is removed from about 150 to 200 mmlength on either side of the weld bead. Thus a size transition exists atthe edges 8 of the mill coating. The welded joint of FIG. 1 is to beprotected by applying a wraparound sleeve to cover the entire baredregion of steel pipes 2, and to overlap onto the mill coating on eitherside of the bared region. This is described with reference to FIGS. 2 to6.

FIG. 2 is a cross-sectional view showing the apparatus according to theinvention surrounding the welded pipes 2. The apparatus comprises ahollow frame 10 surrounding the pipes 2. The frame is mounted on fourwheels 12 which rest against the outer surface of the pipe and allow theframe to be rotated about the pipes in the direction indicated by thearrows D. Mounted on the frame is a covering material (wrapped sheet)delivery device 14 in the form of a spool on which the wrapped sheet 16is rolled, and from which it is delivered to the surface of the pipe 2.This delivery device is described in more detail with reference to FIG.6. Also mounted on the frame 10, dose to, but behind the delivery device14 (as measured in the direction of rotation D), are two rollers 18 and20. These are mounted on the frame 10 by pivoted bars 22 and 24respectively, allowing the rollers 18 and 20 to be moved from a firstposition (not shown) in which they do not press tightly against the pipe2, to a second position (as illustrated) in which they urge against thesheet 16 and pipe 2. The rollers 18 and 20, each comprise siliconerubber, and each rolls around the pipe and presses onto the deliveredsheet 16 as the frame 10 is rotated. The wrapped sheet 16 comprises apolymeric sheet material coated with adhesive which is in turn coveredwith a release layer. This is described in more detail later withreference to FIG. 6b. Therefore as the adhesive coated sheet isinstalled the release layer needs to be pulled off, and reeled up. Thisis achieved by take-up spool 42 for the release paper, spool 42 beingdriven by belt 26 and roller 18, via roller 28.

FIG. 3 is a plan view of the apparatus of FIG. 2. This makes it clearthat roller 18 comprises a single central roller part 18', while roller20 comprises two edge roller parts 20' and no central portion of roller.The purpose of this is so that roller part 18' applies a radial pressureon the portion of the cover 16 covering the weld bead 4, while rollerparts 20' exert a radial pressure on the parts of cover 16 overlyingtransition regions 8 at the edges of the mill coating. The downwardpressure exerted by roller parts 18' and 20' may be the same, but ispreferably different, as appropriate for the different sizes and shapesof the projection of weld bead 4 and transition regions 8. The sweptareas of roller parts 18' and 20' (i.e. the areas rolled when the frame10 is rotated) overlap.

Therefore with reference to FIGS. 2 and 3 operation and installation ofsleeve 16 is achieved by unrolling a short length from the deliveryspool 14, fixing it to a point on the pipe 2, and then rotating theframe 10 in the direction of arrow D. Continued rotation of the framecauses the remainder of the sleeve 16 to unreel slowly from the spool14, and at the same time causes roller parts 18' and 20' to roll aroundthe pipe with the frame and to press radially inwards onto the sleeve 16so that a void free bond between the sleeve 16 and the pipeline 2 isachieved. The bonding may be achieved by an adhesive or sealant coatingon the sleeve 16, or by primer on the pipe in a manner known hitherto.This is not illustrated in FIGS. 2 and 3.

FIGS. 4 and 5 are enlarged plan and side views showing the position ofrollers 18 and 20 relative to the weld bead 4 and transition regions 8.FIG. 4 also makes it dear that the central roller part 18' (acting onthe weld bead 4) leads the edge roller parts 20' (acting on transitionregions 8) as measured in the direction D of rotation of the frame 10.

FIG. 6a is an enlarged sectional view showing the delivery of coveringmaterial 16 to the pipe surface 2. FIG. 6b is an enlarged part sectionalview through the sheet material 16.

Referring to FIG. 6b, the sheet material 16 delivered from the deliveryspool 14 comprises a polymeric sheet material 36 coated with a pressuresensitive adhesive layer 38 which in turn is coated with a release layer40. Turning now to FIG. 6a, as the sheet material 16 is deliveredbetween the pipe 2 and rollers 18 and 20 the release layer 40 is pulledaway and fed onto its own take-up spool 42. Thus as the frame 10 (notshown) is turned in the direction indicated by arrow D (counterclockwise in the drawing) the delivery spool 14, take up spool 42 andalso rollers 18 and 20 also move in the direction of arrow D. The sheetmaterial 36 is however bonded by adhesive 38 to the pipes 2. As theapparatus rotates, therefore, the remainder of the spooled sheet 16unreels from the spool 14 and is similarly pressed against and bonded tothe underlying pipes 2.

FIG. 7 shows an alternative configuration of apparatus. In this case theframe 52 is not a closed loop, but can extend only part way around thesubstrate. It comprises two curved arms 52' and 52" spaced from eachother, and between which the rollers 54 and 56 and other parts (asexplained later) extend. Unlike the rollers 18 and 20 of the embodimentof FIGS. 1 to 5, the rollers 54 and 56 act not only as the pressurerollers on the delivered covering material, but also as wheels orrollers for the frame, i.e. they perform the function also of some ofthe wheels 12 in the embodiment of FIGS. 1 to 5. A further pair ofwheels 58 is also included. Rollers 54 and 56 extend between oppositeends of each of the curved arms 52' and 52", and the pair of wheels 58turn on an axle 60 extending between arms 52' and 52" of the frame, at amid point on the arms 52' and 52". Thus rollers 54 and 56 together withwheels 58 perform the function of wheels 12 of the earlier embodiment. Acovering material delivery device 62, and a release paper take-up spool63 (corresponding to the devices 14 and 42 respectively in the earlierembodiment) are also included, extending between curved arms 52' and 52"of the frame 52.

The roller 54 extends directly between arms 52' and 52" of the frame.Roller 56 in contrast extends between the ends of two bars 62, theopposite ends of which are pivotally connected to one end of each ofcurved arms 52' and 52". The connection is such that bars can pivot inthe plane of the curved arms 52' and 52" between two stop positions, asillustrated by the Arrow P in the Figure (one stop position being shownby dotted lines). This change in position can be carried out by movinghandle 66 (which is fixed to bars 64) in the direction indicated byarrows Q. The effect of this movement is to move the roller 56 from afirst position (as illustrated by the dotted Lines) in which it does notpress against the covering material and underlying pipe, and in whichthe frame can be positioned from the side onto the substrate, to asecond position (as illustrated by the continuous lines) in which theroller presses firmly against the covering material and underlying pipe,and in which the frame is clamped against the pipe, so that firmpressure is exerted by the rollers 54 and 56 as the frame rotates aboutthe pipe, and the frame does not fall off when the frame is rotatedthrough 360° around the substrate.

FIG. 8 shows the apparatus of FIG. 7 positioned over the joint ofFIG. 1. The apparatus is shown in a state ready to deliver the coveringmaterial from delivery device 62 when the frame is rotated in thedirection indicated by arrow D. The handle 66 operating on roller 56 hasmoved roller 56 to the second position in which the rollers 54 and 56and the frame 52 are clamped firmly against the pipe. As will be seenfrom the drawings the frame 52 extends 210° around the pipe (as measuredfrom the center of rollers 54 and 56). Thus when the frame 52 is rotatedthrough 360°, the frame does not fall off the pipe.

FIGS. 9 and 10 are side views of the arrangement of FIG. 8. In FIG. 9the roller 56 is visible, and it can be seen that this in fact comprisestwo roller parts 56' which each act to press over the mill coating edges8, in a similar manner to that described in FIG. 4. FIG. 10 is from thesame view as FIG. 9, but after the apparatus has been rotated indirection of arrow D so that roller 56 is no longer visible, and roller54 is visible. In this case it can be seen that roller 54 comprises asingle central roller part 54, which acts on the weld bead area 4.

We claim:
 1. A method of applying a wrapped covering material around a welded joint between two coated metal pipes bared of coating in the region of the weld, said method comprising:(a) positioning an apparatus comprisingi) a hollow frame which can be positioned around the joint, and which is mounted on two or more wheels or rollers that, in use, can be rolled around the joint causing the frame to rotate around the joint in a circumferential manner; ii) a covering material delivery device mounted on the frame, for receiving a wraparound covering material coated with an adhesive having a tack temperature and for delivering the adhesive-coated covering material onto a surface of the joint as the frame is rotated; iii) at least two pressure rollers which are arranged to press radially inward onto the delivered covering material as the frame is rotated, one roller being arranged to press against the weld region and the other roller acting on the transition between the pipe coating; and iv) a heater for heating the adhesive-coated covering material before it contacts the pressure rollers,said positioning being such that the frame surrounds the joint and the rollers; (b) mounting the adhesive-coated covering material in the delivery device; (c) preheating the joint to 130° to 170° C.; (d) preheating the adhesive-coated covering material to about the tack temperature of the adhesive with the heater; and (e) rotating the frame circumferentially relative to the joint thereby delivering the covering material and causing the pressure rollers to press radially downward so that the roller pressing against the weld exerts a different pressure than the roller pressing against a transition between the pipe coating and the bared pipe.
 2. A method according to claim 1 wherein each roller has a swept area and the swept areas of the rollers are arranged to overlap. 